The present invention relates to a system and method of handling semiconductor wafers and, more particularly, to an apparatus having both a Bernoulli-type pickup wand and a paddle-type pickup and being capable of transferring wafers therebetween.
In the processing of semiconductor devices, such as transistors, diodes, and integrated circuits, a plurality of such devices are fabricated simultaneously on a thin slice of semiconductor material, termed a substrate or wafer. Such wafers are extremely brittle and easily contaminated. During manufacturing of semiconductor integrated circuits, therefore, care must be taken to avoid physical damage and particulate contamination to the wafers.
Various systems are known for handling wafers within semiconductor processing systems. The particular application or environment from which the wafer is lifted often determines the type of pickup device. One class of pickup devices, known as Bernoulli wands, are typically used for high temperature applications. Bernoulli wands utilize jets of gas downward from the wand toward the wafer to create a region of low pressure above the wafer, therefore lifting it. The advantage being that the hot wafer need not contact the pickup wand, except perhaps at one or more small locators depending underneath the wand. Such a Bernoulli wand is shown in U.S. Pat. No. 5,080,549 to Goodwin, et al.
Another type of wafer pickup wand utilizes a vacuum force and thus must be in intimate contact with the wafer. U.S. Pat. No. 4,566,726 to Corenti, et al., discloses a combination Bernoulli and vacuum-type pickup device.
A third type of wafer pickup device is a simple paddle augmented with a vacuum which supports wafers from underneath. Such a paddle is illustrated in U.S. Pat. No. 4,951,601, to Maydan, et al. This patent also illustrates a typical movement device for translating wafers from location to location within processing systems. The wafer handler is capable of linear retraction and extension, as well as rotation about an axis.
U.S. Pat. No. 5,135,349 to Lorenz, et al., discloses a robotic handling system utilizing two paddle style pickups mounted on a common rotating base. Both pickups are adapted to extend linearly away from one another to speed up handling of wafers within the processing system. Again, the paddles are augmented with a vacuum generated through a plurality of holes in an end effector portion of each paddle; the vacuum being transmitted along a channel within the paddle.
There are two main drawbacks to prior wafer handling systems. A single wafer handler may not be appropriate for picking and placing wafers into or out of particular processing environments. That is, a Bernoulli wand might be suitable for high temperature environments, but has a relatively high profile which may limit its maneuverability between closely spaced wafers. Furthermore, rotating handling robots, such as the ones shown in the patent to Maydan, et al., require a significant amount of horizontal room to maneuver. Although the device in the Maydan patent is a multiple chamber processing system, many systems only include a single processing chamber, and thus such a rotational wafer handler is inefficient.
Briefly stated, the invention provides a dual-arm wafer handling assembly that includes a pair of pick-up arms for transferring wafers within a wafer processing system. The two pick-up arms are adapted to move such that the wafer moved by one of the arms can be aligned with the other arm to enable the wafer to be transferred between the two. In one version, a paddle-style pick-up arm is utilized to move wafers into and out of a storage cassette or other area which is usually not highly heated, and then transferred to a Bernoulli wand and moved into and out of another location such as a high temperature process chamber. The two arms preferably move in linear paths with the paddle and a head of the Bernoulli wand being in overlapping position so that a wafer carried by the retracted paddle is moved directly beneath the head of a retracted Bernoulli wand. Gas emanating from the Bernoulli wand is directed onto the wafer and then deflected outwardly to the edges of the wafer and the head of the Bernoulli wand creating a low pressure above the wafer which lifts it from the paddle and allows it to be moved by the Bernoulli wand without having the wafer contacting the Bernoulli wand, except at locator points on the edge of the wafer. In the reverse procedure, a wafer may be transferred from a wand to a paddle.
Advantageously, the Bernoulli wand portions that extend into the process chamber can withstand the high temperatures in the chamber, thus, allowing a wafer to be retracted at a temperature higher than that which can be withstood by the normal paddle materials. Further, even if the paddle is made of material which can withstand high temperatures, it is undesirable to touch the wafer at such elevated temperatures. The paddle, on the other hand can move into and out of standard wafer carriers whereas a Bernoulli wand may be too thick for some.
In one form of the invention, the mechanism for moving the two pick-up arms is controllable to move the arms at varied accelerations and velocities during a process cycle. Thus, in accordance with a method of the invention, the maximum parameters for the pick-up arms with and without a wafer, can be selected.
In another aspect of the invention, the quartz Bernoulli wand head has a unique wafer stop for limiting rearward movement of a wafer. The stop is separately removable from the remainder of the head which enables the stop to be replaced separately as needed.